Electrochemical test sensor with light guide

ABSTRACT

An electrochemical test sensor for detecting the analyte concentration of a fluid test sample includes a base, a dielectric layer, a reagent layer, a light guide area, and a lid. The base provides a flow path for the test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current. The dielectric layer forms a dielectric window therethrough. The reagent layer includes an enzyme that is adapted to react with the analyte. The lid is adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the test sample thereto. The light guide area transmits light towards the capillary space.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage of International Application No. PCT/US2007/025407, filed Dec. 12, 2007, which is related to and claims priority to U.S. Provisional Application Nos. 60/905,421, filed Mar. 7, 2007, and 60/878,953, filed Jan. 5, 2007, which are incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to electrochemical test sensors, and more specifically to a test sensor that is adapted to determine the concentration of an analyte.

BACKGROUND OF THE INVENTION

Medical conditions such as diabetes require a person afflicted with the condition to regularly self-monitor that person's blood-glucose concentration level. The purpose of monitoring the blood glucose concentration level is to determine the person's blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action may have serious medical implications for that person.

One method of monitoring a person's blood glucose level is with a portable testing device. The portable nature of these devices enables users to conveniently test their blood glucose levels at different locations. One type of device utilizes an electrochemical test sensor to harvest and analyze the blood sample. The test sensor typically includes a capillary channel to receive the blood sample and a plurality of electrodes. There are times when a person needs to monitor their blood glucose concentration level in a setting without a great deal of ambient lighting. There are other times when a person who monitors their blood glucose concentration level may have difficulty locating where the blood sample will be collected by the test sensor. Thus, there exists a need for an electrochemical test sensor capable of allowing light to be transmitted through the test sensor to both help the person when testing in an area with low ambient lighting, and allowing the person to know what area of the test sensor the blood sample collection occurs.

SUMMARY OF THE INVENTION

According to one embodiment, an electrochemical test sensor for detecting the concentration of an analyte in a fluid test sample comprises a base, dielectric layer, a reagent layer and a lid. The base provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current. The dielectric layer forms a dielectric window therethrough. The reagent layer includes an enzyme that is adapted to react with the analyte. The lid is adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto. The lid includes a light guide area that transmits light from a first end of the test sensor towards the capillary space.

According to one embodiment, an electrochemical test sensor for detecting the concentration of an analyte in a fluid test sample comprises a base, dielectric layer, a reagent layer, a light guide layer, and a lid. The base provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current. The dielectric layer forms a dielectric window therethrough. The reagent layer includes an enzyme that is adapted to react with the analyte. The lid is adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto. The light guide layer is adapted to transmit light form a first end of the test sensor towards the capillary space. The light guide layer, the dielectric layer, and the reagent layer are located between the base and the lid.

According to one method, an analyte concentration in a fluid sample is determined with a test sensor. An electrochemical test sensor is provided that includes a base, a dielectric layer, a reagent layer, a light guide area, and a lid. The base provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current. The dielectric layer forms a dielectric window therethrough. The reagent layer includes an enzyme that is adapted to react with the analyte. The lid is adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto. The light guide area is adapted to transmit light through the light guide area towards the capillary space. The dielectric layer and the reagent layer are located between the base and the lid. The light guide transmits light through the light guide area towards the fluid sample. The light transmitted through the light guide area illuminates the fluid sample. The reagent layer contacts the fluid sample via the capillary space. An electrical signal is generated in the test sensor in response to the presence of the analyte. A level of the analyte is determined from the electrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an electrochemical test sensor according to one embodiment.

FIG. 2 is a perspective view of the assembled electrochemical test sensor of FIG. 1 in a portion of an illustrative test meter.

FIG. 3 is a top view of the assembled electrochemical test sensor of FIG. 1.

FIG. 4 is an exploded view of an electrochemical test sensor including a spacer according to one embodiment.

FIG. 5 is an exploded view of an electrochemical test sensor including a spacer according to another embodiment.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The present invention is directed to an electrochemical test sensor meter that is adapted to be placed into a meter or an instrument and assist in determining an analyte concentration in a body fluid sample. The electrochemical sensor of the present invention assists in reducing the volume of the fluid sample needed to properly determine the analyte concentration. The body fluid sample may be collected with a lancing device.

Examples of the types of analytes that may be collected include glucose, lipid profiles (e.g., cholesterol, triglycerides, LDL and HDL), microalbumin, hemoglobin A_(1C), fructose, lactate, or bilirubin. It is contemplated that other analyte concentrations may also be determined. The analytes may be in, for example, a whole blood sample, a blood serum sample, a blood plasma sample, other body fluids like ISF (interstitial fluid) and urine, and non-body fluids. As used within this application, the term “concentration” refers to an analyte concentration, activity (e.g., enzymes and electrolytes), titers (e.g., antibodies), or any other measure concentration used to measure the desired analyte.

Referring initially to FIGS. 1-3, an electrochemical test sensor 34 includes an insulating base 36, a meter-contact area 38, a plurality of electrodes 40, 42 and 44, a dielectric layer 48, a reagent layer 52 and a lid 54. The plurality of electrodes in FIG. 3 includes a working electrode 40, a counter electrode 42 and a trigger electrode 44. The electrochemical test sensor 34 may be printed in sequence such as by a screen-printing technique. It is contemplated that the electrochemical test sensor may be formed by other methods.

The lid 54 includes a light guide area 55. The light guide area 55 is translucent or transparent to allow light to transmitted through the light guide area from a first end 74 of the test sensor 34 to a second end 76 of the test sensor. A test meter 80 (a portion of which is shown illustratively in FIG. 2) that the test sensor 34 is placed into features a light source 82 (FIG. 2), such as, for example, a light emitting diode (LED), near where the first end 74 interacts with the test sensor 34. The light from the light source 82 passes through light guide area 55 to the second end 76 of the test sensor 34, illuminating a capillary channel 58 (FIG. 2) of the test sensor 34. By illuminating the capillary channel 58 (FIG. 2), a user may more accurately position the test sensor 34 to a sample to be tested, such as a drop of blood on the users finger.

It is contemplated that the light guide area 55 may vary in width from the first end 74 to the second end 76 of the test sensor 34. The width of the light guide area 55 at the second end 76 of the test sensor 34 may be wider than the width of the light guide 55 are at the first end 74 of the test sensor 34 to allow more light to be visible to a user.

The light guide 55 may be made from a variety of materials. Non-limiting examples of materials to be utilized in forming the light guide 55 include acrylic, Polyethylene Terephthalate (PET), polycarbonate, or any other transparent or translucent polymeric material. Opaque areas surround the light guide 55 to allow a greater amount of light to transmit through the light guide 55.

The function of the reagent layer 52 of FIG. 1 is to convert an analyte (e.g., glucose) in the fluid test sample, stoichiometrically into a chemical species that is electrochemically measurable, in terms of electrical current it produces, by the components of the working electrode 40 and the counter electrode 42. The reagent layer 52 typically includes an enzyme and an electron acceptor. The enzyme reacts with the analyte to produce mobile electrons on the working and counter electrodes 40, 42. For example, the reagent layer may include glucose oxidase or glucose dehydrogenase if the analyte to be determined is glucose. The enzyme in the reagent layer 52 may be combined with a hydrophilic polymer such as poly(ethylene oxide) or other polymers such as polyethylene oxide (PEO), hydroxyethyl cellulose (HEC), carboxymethylcellulose (CMC) and polyvinyl acetate (PVA). The electron acceptor (e.g., ferricyanide salt) carries the mobile electrons to the surface of the working electrode 40.

The dielectric layer 48 of FIG. 1 limits the electrical area that is ultimately formed. Specifically, the dielectric layer 48 of FIG. 1 forms a dielectric window 50 that defines the working electrode 40 and assists in partially defining the counter electrode 42 as will be discussed below. The dielectric window 50 includes a first dielectric window section 50 a, a second dielectric window section 50 b and a third dielectric window section 50 c. The dielectric layer may be formed by a variety of methods such as printing or die-cutting of a pressure-sensitive adhesive. It is contemplated that the dielectric layer may be formed by other methods.

The working electrode 40 and the counter electrode 42 assist in electrochemically determining the analyte concentration. In one embodiment, the working electrode 40 and the counter electrode 42 comprise a mixture of amorphous and graphite forms of carbon that is chosen to be electrochemically active and provide a low electrical resistance path between the electrodes and the meter or instrument with which they are in operative connection via the meter-contact area 38. In another embodiment, the working electrode 40 and the counter electrode 42 comprises a mixture of carbon and silver. It is contemplated that the working electrode and counter electrode may be made of other materials that assist in providing an electrical path to the meter or instrument with which they are in operative connection. It is contemplated that additional conductors may be added. For example, in FIG. 1, first and second conductors 70, 71 comprise a highly conductive carbon-silver ink that may be printed to further reduce the electrical resistance from the working and counter electrodes 40, 42 to the meter-contact area 38.

In the electrochemical sensor 34 of FIG. 1, the optional trigger electrode 44 assists in determining whether a sufficient fluid sample (e.g., blood) has been placed on the electrochemical test sensor 34. It is contemplated that an electrochemical sensor may include other electrodes such as an underfill electrode, hematocrit-detection electrode or other electrodes.

Referring still to FIG. 1, the lid 54 forms a concave space 56 over the base 36 and the components located thereon eventually form a capillary space or channel (see capillary space or channel 58 of FIG. 2). It is contemplated that the entire concave space 56 is part of the light guide 55. The lid 54 may be formed by embossing a flat sheet of deformable material and then joining the lid 54 and the base 36 in a sealing operation. The material forming the lid 54 may be a deformable polymeric sheet material (e.g., polycarbonate or an embossable grade of polyethylene terphthalate), or a glycol modified polyethylene terephthalate. It is contemplated that other materials may be used in forming the lid.

The material forming the lid 54 may be punctured to provide at least one air vent 60 a,b. The air vents 60 a,b are desirably because they assist in preventing or inhibiting air-lock. By preventing or inhibiting air-lock, a fluid sample is better able to enter the capillary channel 58 in a timely manner.

Suitable materials for the insulating base 36 of FIG. 1 include polymeric materials, such as polycarbonate, polyethylene terephthalate, dimensionally stable vinyl and acrylic polymers, and blends thereof. The insulating base may be formed from metal foil structures such as a nylon/aluminum/polyvinyl chloride laminate. It is contemplated that other materials may be used in forming the insulating base.

The lid 54 and the base 36 may be sealed together by a variety of methods. For example, the lid 54 and the base 36 may be sealed together by sonic welding in which the base 36 and the lid 54 are first aligned and then pressed together between a vibratory heat sealing member or horn and a stationary jaw. In this method, the horn is shaped such that contact is made only with the flat, non-embossed regions of the lid 54. Ultrasonic energy from a crystal or other transducer is used to excite vibrations in the metal horn. This mechanical energy is dissipated as heat in the polymeric joint allowing the bonding of the thermoplastic materials. In another method, the lid 54 and the base 36 are joined by using an adhesive material on the underside of the lid 54. It is contemplated that other methods may be used to attached the lid and the base.

Turning now to FIG. 4, an electrochemical test sensor 134 according to another embodiment is shown. The electrochemical test sensor 134 includes the base 36, a meter-contact area 38, the working electrode 40, the counter electrode 42, and the reagent layer 52. The electrochemical test sensor 134 further includes a lid 154, a light guide layer 155, and a spacer 160.

The light guide 155 has a similar purpose to the light guide 55 previously described in connection with FIG. 1. The light guide 155 has a first area 155 a that is generally transparent or translucent, as well as a second area 155 b and a third area 155 c that are generally opaque. Light is guided from a source within a test meter through the light guide 155 towards a capillary channel of the test sensor 134. The light allows a user to better position a sample to be tested relative to the test sensor 134. The light passing through the light guide 155 will also provide a user with more ambient light near the test meter, so that a user may be able to better observe aspects of the testing, such as a size of a blood drop that may be located on a user's finger. The light guide 155 may be made from acrylic, or other polymeric materials.

The spacer 160 includes a spacer opening 162 formed therein. The spacer opening 162 assists in forming the capillary channel or space when the lid 154 is mated with the spacer 160 and the base 36. The electrochemical test sensor 134 functions in much the same way as electrochemical test sensor 34 with the main differences being the method of forming the spacer opening 162 as compared to the concave space 48, and a separate component for the light guide 155.

Referring to FIG. 5, another electrochemical test sensor (electrochemical test sensor 234) is depicted. The electrochemical test sensor 234 functions in a similar manner as discussed above in connection with electrochemical test sensors 34, 134. The electrochemical test sensor 234 is similar to the electrochemical test sensor 134 except that the electrochemical test sensor 234 does not include a dielectric layer, and a light guide area 255 is present in a lid 254 of the test sensor 234, not a separate layer. The light guide area 255 of the lid 254 is transparent or translucent and adapted to guide light through the test sensor 234 towards a capillary channel. The lid 254 has a first opaque area 254 a and a second opaque area 254 b located laterally of the light guide area 255.

It is further contemplated according to an alternative embodiment that a test sensor may contain chemicals that react to generate light that is transmitted through a light guide area of the test sensor. According to such an embodiment, no additional light source within a test meter would be required.

It is also contemplated according to another alternative embodiment that a test sensor adapted for optical testing, as opposed to electrochemical testing, may include a light guide similar to the embodiments depicted in FIGS. 1-5.

Embodiment A

An electrochemical test sensor for detecting the concentration of an analyte in a fluid test sample, the electrochemical test sensor comprising:

a base that provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current;

a dielectric layer forming a dielectric window therethrough;

a reagent layer including an enzyme that is adapted to react with the analyte; and

a lid adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto,

wherein the lid includes a light guide area adapted to transmit light from a first end of the test sensor towards the capillary space.

Embodiment B

The electrochemical test sensor of embodiment A wherein the lid further forms at least one air vent.

Embodiment C

The electrochemical test sensor of embodiment A wherein the light guide area of the lid is transparent.

Embodiment D

The electrochemical test sensor of embodiment A wherein the light guide area of the lid is translucent.

Embodiment E

The electrochemical test sensor of embodiment A wherein the light guide area of the lid comprises a polymeric material.

Embodiment F

The electrochemical test sensor of embodiment E wherein the light guide area of the lid comprises acrylic.

Embodiment G

The electrochemical test sensor of embodiment A wherein the reagent layer includes glucose oxidase.

Embodiment H

The electrochemical test sensor of embodiment A wherein the reagent layer includes glucose dehydrogenase.

Embodiment I

The electrochemical test sensor of embodiment A wherein the volume of the capillary space is less than about 1 μL.

Embodiment J

The electrochemical test sensor of embodiment A further including a spacer, the spacer being located between the lid and the reagent layer.

Embodiment K

An electrochemical test sensor for detecting the concentration of an analyte in a fluid test sample, the electrochemical test sensor comprising:

a base that provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current;

a dielectric layer forming a dielectric window therethrough;

a reagent layer including an enzyme that is adapted to react with the analyte;

a lid adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto; and

a light guide layer adapted to transmit light from a first end of the test sensor towards the capillary space,

wherein the light guide layer, the dielectric layer, and the reagent layer are located between the base and the lid.

Embodiment L

The electrochemical test sensor of embodiment K wherein the light guide layer has a first area that is transparent.

Embodiment M

The electrochemical test sensor of embodiment L wherein the light guide layer has a second area and a third area that are opaque.

Embodiment N

The electrochemical test sensor of embodiment K wherein the light guide layer has a first area that is translucent.

Embodiment O

The electrochemical test sensor of embodiment L wherein the light guide layer has a second area and a third area that are opaque.

Embodiment P

The electrochemical test sensor of embodiment K wherein the lid further forms at least one air vent.

Embodiment Q

The electrochemical test sensor of embodiment K wherein the reagent layer includes glucose oxidase.

Embodiment R

The electrochemical test sensor of embodiment K wherein the reagent layer includes glucose dehydrogenase.

Embodiment S

The electrochemical test sensor of embodiment K wherein the volume of the capillary space is less than about 1 μL.

Embodiment T

The electrochemical test sensor of embodiment K further including a spacer, the spacer being located between the light guide layer and the reagent layer.

Process U

A method for determining the concentration of an analyte in a fluid sample with a test sensor, the method comprising the acts of:

providing an electrochemical test sensor including a base, a dielectric layer, a reagent layer, a light guide area, and a lid, the base providing a flow path for the fluid test sample having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current, the dielectric layer forming a dielectric window therethrough, the reagent layer including an enzyme that is adapted to react with the analyte, the lid being adapted to mate with the base and to assist in forming a capillary space with an opening for the introduction of the fluid test sample thereto, the light guide area being adapted to transmit light through the light guide area towards the capillary space, the dielectric layer and the reagent layer being located between the base and the lid;

transmitting light through the light guide area towards the fluid sample;

illuminating the fluid sample with the light transmitting through the light guide area;

contacting the reagent layer with the fluid sample via the capillary space;

generating an electrical signal in the test sensor in response to the presence of the analyte; and

determining a level of the analyte from the electrical signal.

Process V

The method of process U wherein the analyte is glucose.

Process W

The method of process U wherein the light guide area is part of the lid.

Process X

The method of process U wherein the light guide area is part of a light guide layer.

Process Y

The method of process U wherein the light guide area is transparent.

Process Z

The method of process U wherein the light guide area is translucent.

Process AA

The method of process U wherein the light guide area comprises acrylic.

Process BB

The method of process U wherein the volume of the capillary space is less than about 1 μL.

Process CC

The method of process U wherein the electrochemical test sensor further includes a spacer, the spacer being located between the lid and the reagent layer.

While the invention is susceptible to various modifications and alternative forms, specific embodiments and methods thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms or methods disclosed, but, to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 

The invention claimed is:
 1. A method for determining the concentration of an analyte in a fluid sample with a test sensor, the method comprising: providing a meter having a light source; providing an electrochemical test sensor including a base, a dielectric layer, a reagent, a light guide area, and a lid, the base having a flow path for the fluid test sample, the base having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current, the dielectric layer forming a dielectric window therethrough, the reagent including an enzyme that is adapted to react with the analyte, the lid mating with the base and assisting in forming a capillary space with an opening for the introduction of the fluid test sample thereto, the light guide area having a transparent or translucent polymeric light guide at least partially surrounded by an opaque area, the polymeric light guide being adapted to transmit light therethrough towards the capillary space, the dielectric layer and the reagent layer being located between the base and the lid, the lid including the polymeric light guide and the opaque area; transmitting light through the polymeric light guide from the light source towards the fluid sample to assist a user in positioning the sample with respect to the test sensor; illuminating the fluid sample with the light transmitting through the polymeric light guide; contacting the reagent layer with the fluid sample via the capillary space; generating an electrical signal in the test sensor in response to the presence of the analyte; and determining a level of the analyte from the electrical signal.
 2. The method of claim 1, wherein the analyte is glucose.
 3. The method of claim 1, wherein the light guide area is embedded in the lid.
 4. The method of claim 1, wherein the polymeric light guide is embedded within the lid extending continuously from a first end of the lid to an opposing second end of the lid.
 5. The method of claim 1, wherein the lid further includes at least one air vent proximate the light guide area.
 6. The method of claim 1, wherein the polymeric light guide is formed from at least one of acrylic, Polyethylene Terephthalate (PET), or polycarbonate.
 7. The method of claim 1, wherein the volume of the capillary space is less than about 1 μL.
 8. The method of claim 1, wherein the electrochemical test sensor further includes a spacer, the spacer being located between the lid and the reagent layer.
 9. An electrochemical test system for detecting the concentration of an analyte in a fluid test sample, the system comprising: a meter having a light source; and an electrochemical test sensor including a base, a dielectric layer, a reagent, and a lid, the base having a flow path for the fluid test sample, the base bearing a counter electrode and a working electrode adapted to electrically communicate electrical current, the dielectric layer forming a dielectric window therethrough, the reagent including an enzyme that is adapted to react with the analyte, and the lid mating with the base and assisting in forming a capillary space with an opening for the introduction of the fluid test sample thereto, wherein the lid includes a light guide area with a transparent or translucent polymeric light guide and an opaque area at least partially surrounding the light guide area, the polymeric light guide being adapted to transmit therethrough light generated by the light source from a first end of the test sensor towards the capillary space to assist a user in positioning the sample with respect to the test sensor.
 10. The system of claim 9, wherein the polymeric light guide is formed from at least one of acrylic, Polyethylene Terephthalate (PET), or polycarbonate.
 11. The system of claim 9, wherein the reagent includes glucose oxidase or glucose dehydrogenase.
 12. The system of claim 9, wherein the volume of the capillary space is less than about 1 μL.
 13. The system of claim 9, further including a spacer, the spacer being located between the lid and the reagent.
 14. An electrochemical test system for detecting the concentration of an analyte in a fluid test sample, the system comprising: a meter having a light source; and an electrochemical test sensor including a base, a dielectric layer, a reagent, and a lid, the base having a flow path for the fluid test sample, the base bearing a counter electrode and a working electrode adapted to electrically communicate electrical current, the dielectric layer forming a dielectric window therethrough, the reagent including an enzyme that is adapted to react with the analyte, and the lid mating with the base and assisting in forming a capillary space with an opening for the introduction of the fluid test sample thereto, wherein the lid includes a light guide area with a polymeric light guide embedded within the lid and extending continuously from a first end of the lid to an opposing second end of the lid, the polymeric light guide being adapted to transmit light generated by the light source from a first end of the test sensor towards the capillary space to assist a user in positioning the sample with respect to the test sensor.
 15. A combination of a meter and an electrochemical test sensor for detecting the concentration of an analyte in a fluid test sample, the combination comprising: the meter having a light source; and the electrochemical test sensor including a base, a dielectric layer, a reagent, a lid, and a light guide layer, the base defining a flow path for the fluid test sample, the base having on its surface a counter electrode and a working electrode adapted to electrically communicate with a detector of electrical current, the dielectric layer forming a dielectric window therethrough, the reagent including an enzyme that is adapted to react with the analyte, the lid mating with the base and assisting in forming a capillary space with an opening for the introduction of the fluid test sample thereto, and the light guide layer having a transparent or translucent polymeric light guide at least partially surrounded by an opaque area, the polymeric light guide being adapted to transmit therethrough light generated by the light source from a first end of the test sensor towards the capillary space to assist a user in positioning the sample with respect to the test sensor, the lid including the polymeric light guide and the opaque area, wherein the dielectric layer and the reagent layer are located between the base and the lid.
 16. The combination of the meter and the electrochemical test sensor of claim 15, wherein the lid has at least one air vent adjacent the light guide layer.
 17. The combination of the meter and the electrochemical test sensor of claim 15, wherein the polymeric light guide extends continuously between opposing first and second ends of the lid.
 18. The combination of the meter and the electrochemical test sensor of claim 15, wherein the reagent includes glucose oxidase or glucose dehydrogenase.
 19. The combination of the meter and the electrochemical test sensor of claim 15, wherein the polymeric light guide includes at least one of acrylic, Polyethylene Terephthalate (PET), or polycarbonate.
 20. The combination of the meter and the electrochemical test sensor of claim 15, wherein the volume of the capillary space is less than about 1 μL. 